Knitting machine defective needle detector

ABSTRACT

A circular knitting machine, comprising a device for detecting defective needles by detecting the absence of a needle hook from its proper place. The device is placed at a locality adjacent the circular path of needle travel, and the needles are raised by a cam so that the hook of every good and properly positioned needle intercepts a collimated bead of radiant energy. The beam is not intercepted properly by a needle which has a broken, bent or otherwise defective hook or which, because of broken butt or other causes, has not been raised properly. The detector is connected to an alarm and may also be connected to a conventional stop motion device. Alternatively, a small magnet mounted on a piezoelectric crystal or magnetic pickup is positioned in the proximity of the hooks of the needles which have been raised by the cam referred to above. The magnet will be deflected by each passing needle of proper constitution and attitude in substantially the same manner, but will be deflected differently by a defective needle.

United States Patent McArthur et a1.

[ 51 May 2, 1972 [72] Inventors: Colln S. McArthur; Benny L. Hester,both of Winston-Salem, NC.

[73] Assignee: R. J. Reynolds Tobacco Company, Winston-Salem, NC.

[22] Filed: July 25, 1969 [21] Appl. No.: 844,808

[52] U.S. Cl. ..66/l57 [51] Int. Cl. ..D04b 35/18 [58] Field otSearch..66/157, 163, 165

[56] References Cited UNITED STATES PATENTS 3,496,739 2/1970 Motin eta1. ..66/163 3,065,615 11/1962 Abrams ....66/l66 3,529,445 9/1970 Brose....66/l57 2,165,975 7/1939 Lawson et a1 ....66/157 2,760,363 8/1956 VanAlen et al.... ...66/l57 2,963,890 12/1960 Hoots ..66/l57 OTHERPUBLICATIONS Schwabe, C., Photoelektrische Warenkontrolle AnDoppelzylinder-Antomaten, Wirkerel-und Strickerel-Technik,

Coburg, October 1964, No. 10; Pages 478- 482 Fault Detection On CircularKnitting Machines," Peter Brose; The Hosiery Trade Journal, June 1969;Vol. 76, No. 906, Pages 89- 92.

Primary Examiner-Mervin Stein Attorney-Cooper, Dunham, Henninger & Clark[57] ABSTRACT A circular knitting machine, comprising a device fordetecting defective needles by detecting the absence of a needle hookfrom its proper place, The device is placed at a locality adjacent thecircular path of needle travel, and the needles are raised by a cam sothat the hook of every good and properly positioned needle intercepts acollimated bead of radiant energy. The beam is not intercepted properlyby a needle which has a broken, bent or otherwise defective hook orwhich, because of broken butt or other causes, has not been raisedproperly. The detector is connected to an alarm and may also beconnected to a conventional stop motion device.

11 Claims, 10 Drawing F igurcs PATENTEDMAY 2 I972 SHEET 1 CF 3 ATTOPA/EVKNITTING MACHINE DEFECTIVE NEEDLE DETECTOR BACKGROUND OF THE INVENTIONIn the course of operating circular knitting machines, the needles areraised and lowered by cams and are also acted upon by sinkers, yarn, andthe completed fabric. The needles are thus subjected to substantialstresses and to friction, as a result of which the needles are sometimesdamaged. When such damage occurs, proper knitting is interrupted,wastage of knitted fabric takes place, and further damage to otherneedles or other parts of the knitting machine may result.

There are several weak points in the needles, one of which is the butt.As the butt is acted upon by lowering and raising cams in the course ofknitting, it may break ofi, it may bend, or it may wear excessively. Theneedle then will not be raised and lowered properly and will notproperly engage the yarn being fed to it. Another weak point is theupper end of a knitting needle and particularly the hook. The hook maybe bent or broken off and thus fail to engage yarn being fed to it.

Since it is important to detect defective needles as early as possible,so as to minimize subsequent damages and wastage, there are variousprior art devices for detecting defective needles. At least one deviceis known in the prior art for detecting the absence of a part of aneedle. Such a device is described in the U.S. Pat. No. 2,760,363 to VanAlen et al., and provides a magnetic circuit having a gap through whichthe hook ends of the needles are passed as the needle cylinder rotatesduring knitting. Good needles affect the magnetic circuit in anidentical manner, but a needle with a broken hook introduces lessmagnetic material in the gap and thus affects the magnetic circuitdifferently. However, it has been found that such an arrangement is oflimited sensitivity in detecting many of the more common forms of needledeformations. For example, the device may fail to detect a needle whichis merely bent such that its hook does not face in the proper direction.

Other known prior art devices are designed to detect the presence of aneedle or a part thereof at a place where no part of a needle should be.For example, the device described in the U.S. patent to Hoots, U.S. Pat.No. 2,963,890 is designed to detect needles which have failed to retractdue to broken butts or other causes. The device has a detecting elementpositioned above the normal circular path of the retracted needles. Anon-retracted needle will-physically contact the detecting element andwill deflect it.

Another type device for detecting defective needles, again by detectingthe presence of a needle part at a place where it should not be, isdescribed in the French Patent No. 1,007,430 to Antoine (copy in Class66-157). The device is designed to detect broken hooks or latches byestablishing electrical contact with only the defective needles.

One common disadvantage with the latter two prior art detectors is thatphysical contact between the detecting device and the defective needlesis necessarily involved. Another disadvantage is that they detect notthe primary defect, that is the absence of a critical part of a needlefrom its proper place, but a secondary effect, namely, the presence of aneedle or a part thereof in an improper place. By looking only forsecondary effects of a needle defect, these prior art devices may failto detect certain defects.

SUMMARY OF THE INVENTION The invention is in the field of knittingmachines and particularly circular knitting machines and is directed todetecting defective needles as early as practicable so as to avoidexcessive subsequent damage and wastage due to defective needles.

One embodiment of the detecting device includes a source of radiantenergy for producing a thin collimated beam and a detector, both ofwhich may be mounted outside the circle defined by the hooks of thecircularly arranged needles, so that the beam is substantially tangentto the circle of needles. Preferably at a locality spaced from the pointwhere knitting takes place, the needles may be raised by a special camsuch that when a needle is at the raised position, its hook interceptsand blocks off the beam of radiant energy. If all needles are good andhave their hooks oriented in the proper fashion, the beam is continuallyintercepted and at least partly blocked, and is never allowed to impingeon the detector in full force. If, however, a hook is defective in thatits butt is broken, bent or excessively worn, or its hook is broken,bent out of alignment or otherwise damaged, or if for any other reasonthe needle is not raised properly or its hook is not oriented properly,the beam is not intercepted and impinges on the detector insubstantially full force. Upon impingement of the beam, the detectorgenerates an electrical signal which is appropriately amplified andshaped to be used to activate an alarm indicating that a defectiveneedle is present, and to activate a stopmotion device of conventionaldesign to stop the knitting machine.

Should the beam of radiant energy be somewhat wider than the hooks atthe point where the hooks intercept the beam, or should the beam besomewhat misaligned, relatively small amount of radiant energy willreach the detector with each passing hook which is in the properposition, but a relatively large amount of radiant energy will reach thedetector upon the presence of a defective needle, especially whereneedle profile at the point of inspection is optimized by use of such asthe previously mentioned cam. Threshold discriminating means is providedin the electrical circuit connected to the detector for discriminatingbetween, on the one hand, the small amounts of radiant energy associatedwith good and properly positioned needles and, on the other hand, thelarger amount of radiant energy associated with defective needles.

An alternative device for detecting defective needles includes a smallmagnet positioned near the hook of a nondefective needle when raised,preferably by the special cam referred to above. The magnet is mountedon a stationary transducer for converting mechanical stresses toelectrical energy. Since the needles are usually of steel or othermagnetic material; the magnet will be deflected in substantially thesame fashion by each nondefective needle and the electrical signalsgenerated by the transducer will be substantially identical. Should aneedle be defective, however, its hook will not be in the properposition when the needle is raised by the special cam, and the magnetwill not be deflected or will be deflected difi'erently, resulting in adifi'erent electrical signal generated by the transducer.

The transducer is connected to an electrical network which discriminatesbetween the periodic electrical signals produced by the transducer asnondefective needles are passed by the magnet, and electrical signalsproduced by the transducer when a needle whose hook is absent from itsproper place is passed by the magnet. The electrical network operates analarm and a conventional stop-motion device.

As another alternative, in any of the embodiments discussed above, thespecial cam may be omitted and the detector may be associated with theconventional cam which raises and lowers the needles to do the knitting.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified sideelevational view of a portion of a circular knitting machine showing anapparatus for detecting defective needles constructed in accordance withthe invention.

FIG. 2 is a simplified plan view of the apparatus shown in FIG. 1.

FIG. 3 is an enlarged fragmentary vertical section taken along lines 3-3of FIG. 2.

FIG. 4 is an enlarged simplified fragmentary view of a portion of FIG. 2showing schematically radiant energy generating and detecting devicesand several needles in plan view.

FIG. 5 is a fragmentary perspective view showing a good needleintercepting a beam of a radiant energy and the positions of a set ofradiant energy generating and detecting devices.

FIG. 6 is an enlarged fragmentary perspective view similar to that ofFIG. 5, but showing a needle with broken hook.

FIG. 7 shows schematically an electrical circuit used in connection witha radiant energy detecting device for activating an alarm and astop-motion device.

FIG. 8 is a timing diagram of signals generated by defective needledetecting devices.

FIG. 9 is a simplified plan view, similar to that of FIG. 4, of anembodiment of a defective needle detecting device.

FIG. 10 shows schematically an electrical circuit used in connectionwith the detecting device shown in FIG. 9.

DETAILED DESCRIPTION FIGURES 1 THROUGH 3 A conventional circularknitting machine normally has a stationary bed plate 10 and a needlecylinder 12 guiding a circular row of vertically disposed needles 16. Anannular sinker cap 14 coaxial with the needle cylinder 12 is disposedaround the periphery of the circle defined by the needles 16 adjacentbut below the top ends thereof. The sinker cap 14 supports a number ofindividual sinkers (not shown) which cooperate with the needles 16 toform the fabric.

Each of the needles 16 normally includes a butt 18 (best seen in FIG. 3)which extends outwardly radially from the lower end of the needle, astem 20 extending upwardly from the butt 18, and a hook 22 formed at thetop end of the needle 16 and extending outwardly radially therefrom.Each needle may also have near its upper end a latch 26 pivoted at anaxis 28 for movement up toward the hook 22 and downward away from thehook 22. Although the needles 16 are shown as flat in the radialdimension, they may be of other configurations. For example, the needlesmay be round, or may have square crosssection in the horizontal plane.Commonly, they are made of a suitable grade of steel.

In the course of knitting, the butts 18 of the needles 16 are acted uponby cams to raise the needle or to lower them so as to engage yarn fed tothem. Knitting may take place in the general area indicated at 30 inFIG. 2, but will not be described here in any detail since it isconventional and well known in the art.

In co-acting with the knitting cams, the sinkers, the yarn and thecompleted fabric, the needles 16 are subjected to various stresses andfrictional forces. There are at least two weak points in a needle: thebutt 18 and the hook 22. lfthe butt 18 is bent, broken, or otherwisedamaged, the needles 16 will not be raised and lowered properly duringknitting and will not properly engage yarn at the hook ends. If, on theother hand, the hook 22 is bent, broken or otherwise damaged, theneedles 16 may be properly raised, but will not properly engage yarn.Thus, if either or both the butt l8 and the hook 22 of a needle orneedles are damaged or defective, proper knitting will be prevented andthe result will be knitting of defective fabric or possibly damage toother needles or other parts of the knitting machine.

It is important therefor to detect defective or damaged needles as earlyas possible, and thus the present invention is in a device, indicatedgenerally at 32 in FIG. 2, for detecting defective needles. The device32 uses a thin collimated beam of radiant energy which is intercepted byevery needle hook which is in its proper position as the needle cylinder12 is rotated during knitting and as the needles 16 are raised by aspecial cam 64.

It is possible to position the device 32 so that its beam is alignedwith the needle hooks at the point where they are raised by theconventional knitting cam. However, it is preferred to raise the needlesfor inspection purposes at a point peripherally spaced from the knittingpoint, so as to avoid interference of the yarn or fabric with the beamof radiant energy, as well as to present an optimum profile of thepassing needles to the radiant energy beam.

The detecting device 32 includes a source of radiant energy 50 whichmay, for example, be a light, and a radiant energy detector 52 which maycorrespondingly be a photocell. The source 50 and the detector 52 areeach attached to one of the shoulders of a T-shaped arm 42 by means of abracket 54. Each of the brackets 54 is a rectangular metal strippartially superimposed on the arm 42, then extending around either thesource 50 or the detector 52, and then terminating after extendingpartially along the bottom end surface of the arm 42.

A vertical bolt 56 passes through appropriate apertures in each of thebrackets 54 and through opening 60 in the arm 42. Each of the openings60 is considerably larger in vertical cross-section then the thicknessof the stem of the bolt 56 so as to allow adjustment of the bracket 54and thus of the source 50 or the detector 52 with respect to the arm 42for the purposes of aiming the beam of radiant energy. The bolt 56 issecured by means of a nut 58 positioned below the bracket 54. For aimingin the vertical plane, the bracket 54 may be bent or 'shimmedappropriately.

The source of radiant energy 50, generating a beam 68, and the detector52 are thus in a horizontal plane which is some distance above thesinker cap 14, and the beam 68 travels along a path tangential to acircle 69 defined, in plan view, by the needles 16. As seen in FIG. 3,the width of the beam 68 is somewhat less than the width of the hook 22which intercepts it. A typical beam width may be about twenty-fivethousandths of an inch, while the typical width of the hook at the placewhere it intercepts the beam may be about thirty-two thousandths of aninch. As seen in FIG. 4, the beam 68 is substantially tangent to thecircle defined by the hooks 22 of the needles 16, and is positioned suchthat most of it, if not all of it, is obstructed by a hook 22 of a goodneedle 16 where the needle is in the beams path. It is possible,however, to position the arm 42 such that the source 50 and the detector52 will be in a plane inclined from the horizontal, so long as asubstantial portion of the beam generated by the source 50 is traversedby the hook 22 of nondefective needles 16.

The arm 42 extends radially from the needle cylinder 12 horizontally andis pivoted by means of a pivot shaft 62 and a hinge plate 44 such thatit may be raised up and away from the needle cylinder 12. The hingeplate 44 is attached by means of appropriate screws 44-a and 44-h to avertically disposed stand 34 which is secured at its bottom end to thestationary bed plate 10 by means of a vertical bolt 36. The bolt 36passes through an appropriately sized and countersunk bore 38 in the bedplate 10 and threads into appropriately sized and threaded opening 40 atthe bottom end of the stand 34.

As best seen in FIG. 1, the source 50 and the detector 52 are positionedat a convenient height above the top end of the sinker cap 14, and theretracted needles 16 have their books substantially at the level of thesinker cap 14. A special cam 64, restrained by a cam retainer ring 66,is provided for the purpose of raising the needles such that their hookscome up to the level of the beam of radiant energy between the source 50and the detector 52. The purpose of raising the needles 16 is to insurethat the effect of a broken needle butt 18 will be demonstrated. If abutt 18 is broken or otherwise damaged, its needle 16 will not be raisedby the special cam 64 in the same manner as the good needles, and thisfact will be detected.

FIGURES 4 THROUGH 8 As best seen in FIG. 4, the beam of radiant energyindicated at 68 is substantially tangential in plan view to the circledefined by the hooks 22 of the needles 16. As seen in even greaterdetail in FIGS. 5 and 6, the beam 68 is collimated and is narrower thanthe dimension of the hooks 22 perpendicular to it. If a book 22 isproperly in its position, the beam 68 is blocked off and does not reachthe detector 52. If a hook 22 is broken, however, as shown in FIG. 6 thepath of the beam 68 is not interrupted and it reaches the detector 52.

Any suitable combination of a radiant energy source and a radiant energydetector may be used. One example is a light to be used as the source 50and a photocell to be used as a detector 52. The light beam 68 may becollimated and made sufficiently narrow by conventional means such as bythe use of fiber optics.

Ifall needles 16 have their hooks in the proper position, the beam 68will be substantially blocked off at all times and will never reach thedetector 52 in full force. A part of the beam 68 may however, impinge onthe detector 52 for any number of reasons: the beam may not be perfectlycollimated or aimed, the beam may be somewhat wider than the hook areathat intercepts it, there may be vibration which disturbs the perfectionof alignment between needles and the beam. However, only a small portionof the beam 68 should reach the detector 52 for as long as every needle16 is good and is in its proper position. The effects of this smallportion of radiant energy can be compensated by use of proper electricalcircuitry, as will be explained later in connection with FIGS. 7, 8 and10. As the needle cylinder 12 is rotated, the needle 16 which is in thepath of the beam 68 will start moving out of that path, but the nextneedle 16 will interpose itself between the source 50 and the detector52 before the preceding needle has moved out of the path of the beam 68.

Should one of the hooks 22 not be in its proper position, however, thebeam 68 will no longer be blocked, and it will reach the detector 52 infull force. A hook 22 may be absent from its proper position due to anynumber of causes. Any absence, however, is a defect which ought to bedetected as early as possible.

The source of radiant energy 50 is supplied with power by appropriatewiring (not shown), and the detector 52 is connected by appropriatewiring (again not shown) to an electrical circuit such as the circuitdiagrammatically illustrated in FIG. 7 for the purpose of utilizing thesignals produced by the radiant energy detector 52. If, for example, aphotocell is used as a radiant energy detector 52, it will producedifferent electrical signals depending on the amount and intensity ofthe light that reaches it. The electrical signals produced by thedetector 52 are amplified by an amplifier 70, of conventional design,and are then fed into a threshold gate 72, also of conventional design,which cuts out electrical signals below a certain voltage level andpasses only electrical signals over a certain voltage level.

If a photocell is used as a radiant energy detector 52, the thresholdgate 72 is adjusted such that it cuts out electrical signals generatedby the photocell in response to ambient lighting or to the incidence ofa small portion of the beam 68 as well as electrical signals due tonoise, and passes only electrical signals generated by the photocell inresponse to its being impinged squarely by the light beam 68.

The output'of the threshold gate 72 is delivered to the Set input of aSet-Reset (RS) flip-flop 74, also of standard design. The flip-flop 74is normally at its zero state, that is, there is a steady voltage signalat its output labeled 0 and there is no voltage signal at its outputlabeled 1". When a signal appears at its Set input, that is the inputlabeled S, the I output of the flip-flop 74 will be energized and thevoltage signal therefrom will be delivered to an alarm 76 and to astop-motion control 78.

The alarm 76 may be a light, a bell or any other device for calling theattention of a machine operator to the fact that a needle hook is absentfrom its proper place and a defect is indicated. The stop motion control78 may be any standard device for stopping the motor operating theknitting machine and causing the needle cylinder 12 to stop rotating.

Once the attention of the operator has been obtained, he may then, bymeans of manual reset switch 80 reset the flipflop 74 to its zero state.The alarm 76 may be deactivated by the operator in a conventional mannerand, after the defect has been repaired, the motor operating theknitting machine may be restarted by appropriate manual means.

The electrical signal produced by the detector 52 is illustrated in FIG.8, Graph 82, which is a plot of the voltage output of the detector 52vs. time. The time instances labelled t correspond to the interceptionof the beam 68 by a maximum area of the hooks 22. As one hook beginsmoving out of the beam 68 but prior to the time of another hook comingsquarely in the beam, there may be a small amount of radiant energyreaching the detector 52 and resulting in a small voltage peak at thetime instances indicated at Ifa needle hook is not at its proper place,however, the voltage pealc produced by the detector 52 will be of muchgreater magnitude, as indicated at t, at graph 82. The threshold levelof the threshold gate 72 may be adjusted such that the small voltagepeaks as those indicated at times I, will be cut off and only voltagepeaks such as the one indicated at t will produce output signals at theoutput of the threshold gate 72.

Should the beam 68 be made so narrow, and aimed so perfectly, that it isblocked at all times by passing good needles, then the output of thedetector 52 will be of the shape illustrated in graph of FIG. 8. Up tothe point indicated at 80-a, the graph 80 shows that the path of thebeam 68 is at all times blocked off by a needle hook and the output ofthe detector 52 is only in response to ambient lighting and possiblyincludes some noise.

If a hook 22, however, is absent from its proper place, the beam 68 willnot be blocked and the beam will strike the detector 52. At that time,the voltage output of the detector 52 will have the general shape of thepeak indicated at 804:. When the next good needle moves in the path ofthe beam 68 the beam will again be blocked, and the voltage output ofthe detector 52 will again drop as indicated at 80-0.

The broken line parallel to the time axis indicates the voltage level towhich the threshold gate 72 of FIG. 7 is adjusted in order to cut ofiany signals from the detector 52 resulting from noise or ambientlighting effects. Any voltage above the threshold level results in anoutput signal at the threshold gate 72.

FIGURES 9 AND 10 An alternative device for detecting the absence ofneedle hooks from their proper places is illustrated schematically inFIG. 9. The device includes a magnet 90, which may for example be apennanent magnet of very small mass as to minimize the efl'ects of itsinertia. The magnet is aflixed to a transducer 92 for convertingvariations in mechanical stresses to variations in electrical signalsand may, for example, be a piezoelectric crystal or a magnetic pick-up.The transducer 92 is mounted on a housing 94 which may also serve as ahousing for associated electrical circuitry such as the circuitry shownin block schematic form in FIG. 10. The housing 94 may in turn beappropriately mounted onto a supporting structure similar to the oneused for mounting the radiant energy detecting device discussed above.

As the needles 16, which are normally of steel or other magneticmaterial, pass by the magnet 90 as they are raised by the special cam64, the magnet is deflected by each passing needle from its originalposition at which the crystal 92 is unstressed. If all needles aresubstantially of the same configuration and in substantially the sameposition with respect to the magnet 90 as they pass by it, the magnet 90will be deflected in substantially the same manner by each passingneedle 16. The mechanical stresses on the piezoelectric crystal 92 willthen be substantially the same for each properly positioned and properlyconstituted needle, and the crystal will produce voltage peaks such asthe peaks 84-a, 84-h and 84-c of graph 84 in FIG. 9.

Should a needle hook be absent from its proper place, however, such asschematically illusu'ated at needle l6-a at FIG. 9, the magnet 90 willbe deflected less and the voltage peak produced by the piezoelectriccrystal 92 will be of lesser magnitude as shown at 84-dof graph 84 inFIG. 8.

A conventional demagnetizer 91 energized by a power source 93 may bespaced peripherally from the housing 94 and adjacent to the path of theneedles 16 to remove from the needles any residual magnetization whichmay cause a latch 26 to stick improperly to a hook 22 or a stem 18. Thedemagnetizer 91 and the power source 93 may be appropriately supportedon the bed plate 10.

The electrical circuitry associated with the crystal 92 is shown in FIG.10 where the crystal is shown as block 92 labeled DETECTOR. The voltageoutput of the crystal 92 which is of the shape illustrated at graph 84of FIG. 8 is delivered to a conventional amplifier 93 and the output ofthe amplifier is delivered to the input of a one-shot multivibrator 96which has adjustable time constant.

The multivibrator 96 is of standard design, with complementary and loutputs and a pulse input, and its characteristics are such that whenpulsed at its input by a voltage pulse of sutficient magnitude, itproduces a voltage level at its output labeled l for a time intervaldefined by its time constant. The amplifier 93 is adjusted such thatvoltage peaks such as 84-a, 84-b and 84-c of FIG. 8 correspond tovoltage signals at the output of the amplifier 93 whose magnitude isjust sufficient to trigger the multivibrator 96, but voltage peaks oflesser magnitude do not result in signals able to trigger themultivibrator 96.

If the multivibrator 96 is pulsed by a sufliciently strong voltagesignal during the time interval defined by its adjustable time constant,a new time interval begins. If it is not pulsed during that timeinterval, the voltage level at its 1 output drops to 0 and a voltagesignal appears at its output labeled 0". The 0 output of themultivibrator 96 is connected to an alarm 76 and to a stop-motioncontrol 78 which are similar to and operate similarly as the alarm andthe stop-motion device shown in FIG. 7 and discussed in connectionthereto.

Thus, if every needle passing by the magnet 90 has its hook in theproper position, the transducer 92 will keep producing voltage pulsessuch as those illustrated at 84-a, 84-h and 84-c in FIG. 8 and themultivibrator 96 will be pulsed before its time interval ever gets achance to run out. But, if there is a dcfective needle which does nothave its hook at the proper place, the signal produced by the transducer92 will be of the general shape illustrated at 84-41 in FIG. 8 (i.e.,insufficient to trigger the multivibrator 96) and the time constant ofthe multivibrator 96 will run out before the next adequate pulse 84-ecomes about.

When the time interval of the multivibrator 96 runs out before itreceives an adequate triggering pulse, a voltage signal appears at its 0output and the alann 76 and the stop-motion control 78 are activated inthe same manner as described in connection with FIG. 7.

An electrical circuit such as the one shown in FIG. 10 may also be usedin conjunction with a radiant energy device for detecting defectiveneedles, if the radiant energy beam 68 is not tangential to the circleof needle hooks but is in a different plane. For example, if the beam 68is in a plane perpendicular to the plane defined by the circle of needlehooks then, provided an inverter is connected to the output of thedetector 52, the signals at the output of the inverter will be of theshape illustrated in graph 84 of FIG. 8 and defective needles can bedetected by operating the circuit of FIG. 10 similarly to its operationin conjunction with the detecting device of FIG. 9.

When a knitting machine equipped with a defective needle detector asdescribed above is turned on after having been stopped, the operation ofthe detector may be delayed until the needles reach their steady statespeed so as to avoid undesirable transient efiects. To this end, themachine operator may turn on the detector manually several seconds afterthe knitting machine motor has been turned on. Preferably, however, thepower line to the detector is connected to a conventional time delayrelay (not shown) which is energizable upon turning on the knittingmachine motor to connect power to the detector for a predetermined timedelay allowing the needles to reach steady state speed.

We claim:

1. Apparatus for detecting defective needles in a knitting machinehaving a regular array of needles, comprising:

a. means for generating a beam of radiant energy;

b. means for producing relative motion between the beam and the needlesso that the needles successively intersect and at least partially blockthe beam;

c. means for detecting the beam, said means located on the opposite sideof the intersecting needles from the generating means, said detectingmeans producing a signal varying as a function of the radiant energyimpinging thereon; and

d. means responsive to an irregular variation in said signal forindicating that a needle is defective.

2. Apparatus as in claim 1 including:

d. means for discriminating between, on the one hand, a first signalproduced by the detecting means while said beam is intersected by aneedle which is in its proper position, and, on the other hand, a secondsignal produced by the detecting means while said beam is directedtoward the proper position of a needle which is not in its properposition; and

e. an alarm and a stop-motion device, each energizable by saiddiscriminating means upon the detection by said discriminating means ofsaid second signal.

3. Apparatus as in claim 1 wherein said generating and said detectingmeans are positioned for directing the beam of radiant energy along apath intersected by the needle hoods, said detecting means producing afirst type signal to correspond to a needle which has its hook in thenormal position while intersecting the beam and producing a second typesignal to correspond to a needle whose hook is absent from its normalposition.

4. Apparatus as in claim 1 wherein said needles are in a circulararrayof needles, and includin g:

a. means for rotating the needle array with respect to the beam andmeans for raising needles successively as the circular array of needlesis rotated; and wherein b. the generating and the detecting means arepositioned for directing the beam of radiant energy along a pathintersected by the hooks of the needles as they are raised successivelyby said raising means.

5. Apparatus as in claim 1 wherein means is provided for collirnatingthe beam of radiant energy to a width less than the width of a needle atthe point where the beam is intersected by the needles.

6. Apparatus as in claim 1 wherein said array of needles is a circulararray and including means for supporting said generating means and saiddetecting means entirely outside the space defined by said circulararray of needles.

7. Apparatus as in claim 6 wherein said beam is parallel to a tangent ofsaid circular array of needles.

8. Circular knitting apparatus, including a stationary support, acircularly disposed array of vertically movable needles of magneticmaterial, each needle having a hook at its top end, and means forrotating said array of needles; the improvement comprising:

a. magnet means for generating a magnetic field intercepting the arrayof needles, said magnet means positioned near the normal path of travelof the needles as they are rotated;

b. a transducer for converting mechanical stresses to electrical energy,said transducer being rigidly connected to said magnet means; and

c. means connected to said stationary support for supporting thetransducer,

whereby said magnet means is affected in substantially the same mannerby each passing needle which is in its proper position and is affectedin a different manner by a passing needle which is not in its properposition, and whereby said transducer produces a first electrical signalin response to passing needles which are in their proper positions and asecond, distinctively different electrical signal in response to needleswhich are not in their proper positions.

9. Apparatus as in claim 8 wherein said magnet means is positionedadjacent the normal path of travel of the needle b. means forpositioning said magnet means adjacent the normal path of the hooks ofthe raised needles,

whereby needle defects afi'ecting the ability of a hook to be properlyraised are detected.

11. Apparatus as in claim 8, including demagnetizing means positionedalong the path of the needles past said magnet for removing residualmagnetism from the needles.

l l i

1. Apparatus for detecting defective needles in a knitting machinehaving a regular array of needles, comprising: a. means for generating abeam of radiant energy; b. means for producing relative motion betweenthe beam and the needles so that the needles successively intersect andat least partially block the beam; c. means for detecting the beam, saidmeans located on the opposite side of the intersecting needles from thegenerating means, said detecting means producing a signal varying as afunction of the radiant energy impinging thereon; and d. meansresponsive to an irregular variation in said signal for indicating thata needle is defective.
 2. Apparatus as in claim 1 including: d. meansfor discriminating between, on the one hand, a first signal prodUced bythe detecting means while said beam is intersected by a needle which isin its proper position, and, on the other hand, a second signal producedby the detecting means while said beam is directed toward the properposition of a needle which is not in its proper position; and e. analarm and a stop-motion device, each energizable by said discriminatingmeans upon the detection by said discriminating means of said secondsignal.
 3. Apparatus as in claim 1 wherein said generating and saiddetecting means are positioned for directing the beam of radiant energyalong a path intersected by the needle hoods, said detecting meansproducing a first type signal to correspond to a needle which has itshook in the normal position while intersecting the beam and producing asecond type signal to correspond to a needle whose hook is absent fromits normal position.
 4. Apparatus as in claim 1 wherein said needles arein a circular array of needles, and including: a. means for rotating theneedle array with respect to the beam and means for raising needlessuccessively as the circular array of needles is rotated; and wherein b.the generating and the detecting means are positioned for directing thebeam of radiant energy along a path intersected by the hooks of theneedles as they are raised successively by said raising means. 5.Apparatus as in claim 1 wherein means is provided for collimating thebeam of radiant energy to a width less than the width of a needle at thepoint where the beam is intersected by the needles.
 6. Apparatus as inclaim 1 wherein said array of needles is a circular array and includingmeans for supporting said generating means and said detecting meansentirely outside the space defined by said circular array of needles. 7.Apparatus as in claim 6 wherein said beam is parallel to a tangent ofsaid circular array of needles.
 8. Circular knitting apparatus,including a stationary support, a circularly disposed array ofvertically movable needles of magnetic material, each needle having ahook at its top end, and means for rotating said array of needles; theimprovement comprising: a. magnet means for generating a magnetic fieldintercepting the array of needles, said magnet means positioned near thenormal path of travel of the needles as they are rotated; b. atransducer for converting mechanical stresses to electrical energy, saidtransducer being rigidly connected to said magnet means; and c. meansconnected to said stationary support for supporting the transducer,whereby said magnet means is affected in substantially the same mannerby each passing needle which is in its proper position and is affectedin a different manner by a passing needle which is not in its properposition, and whereby said transducer produces a first electrical signalin response to passing needles which are in their proper positions and asecond, distinctively different electrical signal in response to needleswhich are not in their proper positions.
 9. Apparatus as in claim 8wherein said magnet means is positioned adjacent the normal path oftravel of the needle hooks, whereby said transducer produces a firstelectrical signal to correspond to needles which have their hooks in theproper position, and a second electrical signal to correspond to needleswhose hooks are absent from their normal positions.
 10. Apparatus as inclaim 8 including: a. means for raising the needles as they approach themagnetic means; and b. means for positioning said magnet means adjacentthe normal path of the hooks of the raised needles, whereby needledefects affecting the ability of a hook to be properly raised aredetected.
 11. Apparatus as in claim 8, including demagnetizing meanspositioned along the path of the needles past said magnet for removingresidual magnetism from the needles.